Exhaust diffuser and silencer for inboard motor boats



J. A; SCHELF 3,121,469

EXHAUST DIFFUSER AND SILENCER FOR INBOARD MOTOR BOATS Feb. 18, 1964 Filed Jan. 23, 1961 IN VEN TOR. JOSEPH A. SCHELF AT TOR NE Y6 United States Patent 3,121,469 EXHAUST DIFFUSER AND SILENCER FOR INBOARD MOTOR BOATS Joseph A. Schelf, Jackson Heights, N.Y., assignor of twenty percent to Hugo M. Wikstrom, Port Washington, N.Y., and eighty percent to Cap Schelf and Associates, Incorporated, New York, N.Y., a corporation of New York Filed Jan. 23, 1961, Ser. No. 84,247 5 Claims. (Cl. 181--64) This invention relates to inboard motor boats and, more particularly, relates to an exhaust diffuser and silencer for such boats.

In the most popular type of inboard motor boat construction, the exhaust pipes are led aft and pass through the transom above the waterline. The waste gases from the inboard engines, such as gasoline or diesel engines, are exhausted through the exhaust pipes.

Water is admitted to the jackets of the engine from the sea and, after being used to cool the engine, the hot water is fed into the exhaust pipes and dumped overboard with the exhaust gases.

However, the steam generated by the hot water and the hot exhaust fumes tend to rise immediately, and, due to the partial vacuum created by the moving boat, the steam or water vapor and gases are drawn into the cockpit over the transom. This condition has been a serious drawback to pleasure boating. Under certain conditions, the cockpit, cabins and passengers become soaked by the water vapor. The noxious exhaust fumes further aggravate the passengers.

Additionally, the exhaust noise is usually quite noticeable near the transom, forcing the occupants to shout to be heard.

It is, therefore, the primary object of this invention to provide an exhaust diffuser which will disperse exhaust gases and inhibit any rise of the exhaust gases and water vapor above the transom.

It is a further object of this invention to provide a diffuser which will assist in silencing the exhaust of an inboard power boat.

Other objects and advantages will be pointed out hereinafter.

In accordance with these objects, there is provided, in a preferred embodiment of this invention, an exhaust diffuser comprising a housing fitted to the exhaust pipe of an inboard motor boat. The housing is formed to deflect the exhaust downwardly toward the water. Rotatably mounted in the housing is an impeller comprising a plurality of blades rotatably mounted on a shaft extending transversely of the boats keel. The impeller is provided with an odd number of blades so positioned with respect to the exhaust gases and water as to be rotatably driven thereby. It is usually advantageous to position the impeller with the bottom blades exposed to increase the rotational speed of the impeller by the draft created by boat movement.

The cooling water exhausted through the exhaust pipe is broken up into a spray by the impeller, simultaneously cooling both the exhaust gases and the water to such temperature as to allow it to be dispersed upon the sea and preventing rising of the exhaust gases above the transom height. In addition, the impeller may create a turbulent condition of the exhaust gases which will assist in holding the exhaust gases to a low level on the surface of the sea in which the boat is operating. It is probable that a combination of two effects is obtained but, at any rate, it is clear that the dissipation of the exhaust fumes and water vapor is accomplished.

This invention may be more clearly understood by reference to the following description taken in conjunction with the accompanying drawings, of which:

3,121,469 Patented Feb. 18, 1964 FIG. 1 is a partially sectioned view of one embodiment of this invention installed on a power boat;

FIG. 2 is a sectioned view taken along lines 22 of FIG. 1; and

FIG. 3 is a sectioned view of another embodiment of this invention.

Referring to FIGS. 1 and 2, there is shown a power boat transom 10. Extending through the transom is exhaust pipe 12 through which is exhausted both the exhaust gases of an inboard motor and the hot water, drawn in from the sea and used to cool the inboard engine.

The diffuser 14 is mounted on the terminal end of the exhaust pipe by a plurality of set screws 16 and sealed thereto by an annular gasket 18 fixedly mounted within the diffuser.

The diffuser comprises a housing 20 which may conveniently be a bronze casting. The casting may, of course, be made for each exhaust pipe size. However, I have found it convenient to provide within the casting an internal diameter defined by the enlarged annular section 22 which may be drilled out for the respective exhaust pipe sizes to provide an inlet aperture. The housing extends from said annular inlet aperture in a chamber terminated by cylindrical exit aperture 24 angled away from the axis of said pipe. Mounted within the exit aperture 24 is an impeller 26 consisting of a rotatably mounted shaft 28 having a plurality of blades 30 affixed thereto.

In the embodiment shown there is provided a shaft 32 fixedly mounted within the housing 20 and a concentric Teflon bushing 34 upon which hollow shaft 28 is rotat ably mounted. The shaft 28 is of pentagon shape carrying impellerblades 30 on each flat thereof. By virtue of such construction the forces exerted on the impeller by the-exhaust gases and cooling water, the direction of which is illustrated by arrows 4t) and 38 respectively, is unbalanced, causing rotation of the impeller. An odd number of blades (in the embodiment shown, five blades) are employed. By such provision one blade 36 extends externally of the housing into the air stream illustrated by arrow 42 created by passage of the boat through the air thus augmenting the rotative force on the impeller.

The cooling water exhausted through the exhaust pipe is thrown back into the exhaust gases in a spray by the impeller, which spray has the dual advantage of cooling the water and the exhaust fumes passing through the exhaust pipe within the chamber. For example, the exhaust water, normally at degrees, was cooled to 60 degrees after installation of the diffuser. Similarly, the spray of this cooled water cools the exhaust gases. The cooled gases are then directed downwardly by the bend of the diffuser and spreads both the exhaust gases and the'water vapor on the surface of the sea on which the boat is traveling.

The water vapor and the exhaust fumes remain at the surface of the sea, rising only a few inches in height. This condition continues for a sufficient length of time so that the boat can move ahead of the exhaust fumes, preventing the entry of water vapor and exhaust fumes into the cockpit of the craft. With the diffusers installed it has been found that even on cold, calm days the cockpit will remain dry and free from exhaust fumes. The reason for the desirable dispersion of the exhaust is in large measure believed attributable to the cooling of the exhaust gases and water, thus inhibiting the formation of steam and water vapor and inhibiting thermal rising of the gases.

In addition, the blades of the impeller always partially close the exhaust pipe serving as a very effective silencer of the inboard motors. The violent exhaust popping usually found on boats is considerably cut down to the extent to allow people. sitting in the stern of the boat to converse in normal tones.

The provision for the odd number of blades prevents a hanging condition ensuring rotation of the impeller both while the motors are idling and While underway. When the craft is underway the wind force on the impeller blade 36 extending outside of the housing of the difiEuser provides suificient drive for the impeller as to cause a.

certain amount of turbine effect augmenting the How of exhaust gases from the exhaust pipe. For example, when the diffuser is installed, a gain of about 125 rpm. at normal cruising throttle setting is obtained. This is in significant contrast to conventional mulilers which will create a drop in r.p.m. of about the same order of magnitude.

In addition to the advantages above noted, the diffuser will prevent the entry of water into the exhaust pipe, as for example during a following sea. Thus, the diffuser will prevent engine damage froma following sea where the engines are installed at or below the waterline.

In FIG. 3 there is shown another embodiment of the present invention utilizing a three-bladed impeller. The impeller blades 42. are mounted on the hats of a triangular shaft 44; The shaft 44 is rotatably mounted on a Teflon bushing as set forth in the explanation of the embodiment shown in FIGS. 1 and 2. The three-bladed impeller also serves the purpose of dissipating the fumes and Water vapor. However, since the exhaust pipe is not closed as effectively as with a five-bladed impeller, the silencing efiect is not as great as that noticed with the embodiment shown in FIGS.- 1 and 2.

This invention may be variously embodied and modified within the scope of the subjoined claims.

What is claimed is:

l. A diffuser for use with an exhaust pipe through which is vented both hot exhaust gases and hot water comprising a housing, said housing having an inlet aperture. coupled to said pipe to receive the gases and water vented through said pipe, said housing extending from'said inlet aperture in a chamber terminating in an exit aperture angled away from the axis of said. pipe, an impeller rotatably mounted within said exit aperture, the axis of rotation of said impeller being transverse to the axis of said pipe, said impeller being positioned sothat the vented water and gas will impinge on said impeller to rotatably drive said impeller, the rotation of said impeller throwing said Water into said exhaust gases in a spray thereby to cool said water and gases within said chamber.

' 2. A diffuser in accordance with claim 1 in which said impeller is provided with a central shaft, and blades afiixed to said shaft, said blades being offset from radii of said shaft in a direction opposite to rotation of said impeller.

3. A diffuser in accordance with claim 1 in which said impeller is provided with a central shaft and a plurality of blades affixed to said shaft, said plurality being an odd number.

4. A diffuser in accordance with claim 1 in which said impeller extends externally of said housing.

5. A diffuser for inboard engine motor boats having an exhaust pipe to vent hot gases and hot water from said engine through the transom of said boat comprising a housing, said housing having an inlet aperture coupled tosaid pipe to receive the gases and Water vented through said pipe, said housing extending from said inlet aperture in a downwardly extending chamber terminating at an exit aperture angled away from the axis of said pipe, a bladed impeller rotatably mounted within said exit apertore, the axis of rotation of said impeller being below the axis of said pipe so that said received water and gases will impinge on the upper blades of said impeller to rotatably drive said impeller, the rotation of said impeller throwing said water into said exhaust gases in a spray thereby to cool said water and gases within said chamber,

said. blades being dimensioned to substantially close saidexit aperture thereby to block entry of Water from a breaking stern wave from entering said exhaust pipe.

References Cited in the file of this patent UNITED STATES PATENTS 1,356,189 Castets Oct. 19, 1920 2,678,067 Russell May 11, 1954 FOREIGN PATENTS 35,798 France Nov. 19, 1929 639,546 France Nov. 19, 1929 1,112,595 France Nov. 16, 1955 1,173,458 France Oct. 27, 1958 

1. A DIFFUSER FOR USE WITH AN EXHAUST PIPE THROUGH WHICH IS VENTED BOTH HOT EXHAUST GASES AND HOT WATER COMPRISING A HOUSING, SAID HOUSING HAVING AN INLET APERTURE COUPLED TO SAID PIPE TO RECEIVE THE GASES AND WATER VENTED THROUGH SAID PIPE, SAID HOUSING EXTENDING FROM SAID INLET APERTURE IN A CHAMBER TERMINATING IN AN EXIT APERTURE ANGLED AWAY FROM THE AXIS OF SAID PIPE, AN IMPELLEER ROTATABLY MOUNTED WITHIN SAID EXIT APERTURE, THE AXIS OF ROTATION OF SAID IMPELLER BEING TRANSVERSE TO THE AXIS OF SAID PIPE, SAID IMPELLER BEING POSITIONED SO THAT THE VENTED WATER AND GAS WILL IMPINGE ON SAID IMPELLER TO ROTATABLY DRIVE SAID IMPELLER, THE ROTATION OF SAID IMPELLER THROWING SAID WATER INTO SAID EXHAUST GASES IN A SPRAY THEREBY TO COOL SAID WATER AND GASES WITHIN SAID CHAMBER. 